Temperature adjusting device for an LED light source

ABSTRACT

A temperature adjusting device of the present invention is provided with: LED light sources  11   r,    11   g  and  11   b;  a temperature sensor  9  for detecting an ambient temperature of each of the LED light sources  11   r,    11   g  and  11   b;  a cooling fan  20  for cooling the LED light sources  11   r,    11   g  and  11   b;  a driving circuit  22  for driving the cooling fan  20;  and a control unit  4  which on/off controls a voltage to be applied to the cooling fan  20  so as to set the ambient temperature within a predetermined range based upon results of detection by a temperature sensor  9,  and in this arrangement, upon on/off controlling the applied voltage, the control unit  4  is allowed to gradually raise/lower the applied voltage.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a temperature adjusting device for anLED light source that is provided with an LED light source, atemperature sensor for detecting an ambient temperature of the LED lightsource, a cooling fan for cooling the LED light source, a drivingcircuit for driving the cooling fan, and a control unit which on/offcontrols a voltage to be applied to the cooling fan so as to set theambient temperature within a predetermined range based upon the resultsof detection by the temperature sensor.

[0003] 2. Description of the Related Art

[0004] With respect to a light source used in a copying machine, animage-reading apparatus and the like, after turning the light source on,a temperature rise tends to occur due to self heat generation to causechanges in the light source characteristics and the resulting adverseeffects in image quality of a read image. For this reason, a devicewhich carries out temperature adjustments so as to adjust the ambienttemperature (environmental temperature) of the light source within apredetermined temperature range by using a heater and a cooling fun havebeen proposed. For example, JP-A No. 2-267541 has been known as such adevice using a fluorescent lamp as the light source.

[0005] Further, in a photographic processing device for formingphotographic prints, a scanner for reading frame images formed in adeveloped negative film has been used. With respect to a reading lightsource for use in this scanner, a halogen lamp has been generally used.Here, those light sources using an LED light source have also been knownfrom the viewpoints of its long life and elimination of the need forexchanging the light sources. For example, JP-A No. 2002-365735 hasdisclosed such a photographic film reading device.

[0006] In the case when an LED light-source is used, the LED issubjected to changes in characteristics in the light amount andwavelength depending on temperatures and the subsequent changes in thereading performance; therefore, it is necessary to carry out temperatureadjustments. In order to carry out the temperature adjustments, atemperature sensor for detecting the environmental temperature at whichthe LED light source is placed is installed, and when the presettemperature range is exceeded, a cooling fan is turned on so as to lowerthe temperature. When the temperature is cooled to a preset temperature,the cooling fan is turned off.

[0007] However, the control method for on/off controlling theabove-mentioned cooling fan has the following problems. Since, uponturning the cooling fan n, the LED is quickly cooled, thecharacteristics of the LED tend to deviate. LED light sources of threecelors are required in order to read an image of a color photographicfilm; however, when there are deviations in the characteristics, adverseeffects are caused on the reading performances. Moreover, when thecooling fan is quickly turned on and off, changes in noise are offensiveto the ear, and make the workers uncomfortable.

[0008] When a halogen lamp is used as the light source, a cooling fan isalso used; however, since the halogen lamp is less susceptible tochanges in characteristics due to the ambient temperature, the coolingfan can be continuously rotated without the necessity of turning on andoff. When the cooling fan is continuously rotated, the noise from thefan is not offensive to the ear. In the case of the LED light source,however, since the characteristics thereof are changed depending on theambient temperature, it is not possible to keep the cooling fan rotatingall the time.

[0009] The present invention has been devised so as to solve theabove-mentioned problems, and its objective is to provide a temperatureadjusting device for an LED light source which, upontemperature-adjusting the LED light source by using a cooling fan,neither causes unnecessary deviations in characteristics in the LED, normakes the workers uncomfortable due to abrupt changes in noise.

SUMMARY OF THE INVENTION

[0010] In order t achiev th above-mentioned objective, a temperatureadjusting device for an LED light source in accordance with the presentinvention is provided with an LED light source, a temperature sensor fordetecting an ambient temperature of the LED light source, a cooling fanfor cooling the LED light source, a driving circuit for driving thecooling fan, and a control unit which on/off controls a voltage to beapplied to the cooling fan so as to set the ambient temperature within apredetermined range based upon the results of detection by thetemperature sensor, and in this arrangement, upon on/off controlling theapplied voltage, the control unit is allowed to gradually raise/lowerthe applied voltage.

[0011] In this arrangement, the control unit which on/off controls thevoltage to be applied to the cooling fan is installed. Moreover, uponturning the voltage to be applied on from the off-state, the voltage isnot applied abruptly as a target voltage, but applied as a graduallyincreasing voltage toward the target voltage. With this arrangement, thenumber of revolutions of the cooling fan is gradually increased so thatthe LED is not cooled abruptly. Moreover, noise, generated by thecooling fan, gradually increases so that it is possible to avoid makingthe workers uncomfortable. In the same manner, upon turning the voltageto be applied off from the on-state, the applied voltage is graduallylowered. As a result, it is possible to provide a temperature adjustingdevice for an LED light source which neither causes unnecessarydeviations in characteristics in the LED, nor makes the workers uncmfortabl due to abrupt changes in nois .

[0012] With respect to a preferred embodiment of the present invention,th above-mentioned LED light source is preferably used as a scanner-uselight source used for reading frame images of a photographic film.

[0013] In particular, in the case when a color photographic film isread, LED light sources of three colors are required; therefore, whenthere are deviations in characteristics of the respective LEDs, adverseeffects might be given to image quality of a read image. In other words,in the case when an LED light-source is used as a scanner-use lightsource used for reading a photographic film, the arrangement of thepresent invention particularly exerts superior effects.

[0014] In another preferred embodiment of the present invention, theabove-mentioned LED light source is formed into a line shape along thewidth direction of a photographic film that is to be read, and aline-shaped heater to be placed in parallel with the line direction ofthe LED light source is prepared, and in this arrangement, the controlunit turns the above-mentioned heater off in synchronism with theturning-on of the LED light source, while it on/off controls theabove-mentioned cooling fan irrespective of the turning on/off of theheater.

[0015] In order to appropriately carry out temperature adjustments ofthe LED light source, the temperature control is preferably carried outto an environmental temperature slightly higher than the temperature ofa room in which the scanner is placed. In other words, in the case whenthe environmental temperature is set t a temperature low r than the roomtemperature, since the temperature is always influenced by the roomtemperature, the blower fan needs to be continuously set to theon-state. Here, in such a cooling method, the environmental temperatureinside the LED unit is susceptible to irregularities. As a result, it isnot possible to stabilize the light emission of the LED so that thismethod is not suitable for the formation of a photographic image thatneeds to be dealt as high image-quality data. With respect to the supplyends of the photographic processing devices, there are warm areas andcold areas, and when all those supply ends are taken into consideration,the environmental temperature of the LED needs to be set to, forexample, a temperature slightly higher than the temperature (orrecommended environmental temperature of the machine) of a warm area.

[0016] In this case, when the reading operation for a photographic filmis started, it is preferable to preliminarily set the temperature to adesired environmental temperature. Therefore, the line-shaped heater isplaced adjacent to the line-shaped LED light source, and prior to theapplication of the LED light source, the heater is used to heat the LEDlight source to be set to the desired environmental temperature. Whenthe LED light source is actually turned on, the heater is turned off.After turning the LED light source on, since the LED itself generatesheat, it is not necessary to turn the heater on. In other words, when thLED light source is off, heat is generated by the heater, and when theLED light source is n, heat is generated by the LED light source itself.Therefore, irrespective of the turning on/off of the heater, the settingof the environmental temperature is carried out with high precision byon/off controlling the cooling fan.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view that shows a structure of a scannerdevice in which an LED light source is used.

[0018]FIG. 2 is a block diagram that explains a temperature adjustingdevice of the LED light source and functions thereof.

[0019]FIG. 3 is a graph that explains the contents of the temperatureadjusting process.

[0020]FIG. 4 is a time chart in the case when the scanner is used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Referring to Figures, the following description will discusspreferred embodiments of a temperature adjusting device for an LED lightsource in accordance with the present invention. FIG. 1 is a perspectiveview that shows a structure of a scanner device in which an LED lightsource is used. FIG. 2 is a block diagram that explains a temperatureadjusting device of the LED light source and functions thereof.

[0022] <Structure of Scanner Device>

[0023] This scanner device 1 is used for reading frame images formed ina photographic film F, such as a negative-working film and apositive-working film, to form electronic data. With a transporting faceon which a photographic film F is transported being sandwiched inbetween, LED light sources 11 r, 11 g and 11 b serving as reading lightsources are placed on one side, and a CCD line sensor 2 serving as areading sensor is placed on the other side. The red LED light source 11r, the green LED light source 11 g and the blue LED light source 11 bare installed in order to acquire color image data from the colorphotographic film. The respective LED light sources are formed in a lineshape in association with the line-shaped CCD line sensor 2.

[0024] In comparison with a case in which a halogen lamp is used as thelight source, the LED light source has a longer service life, and alsohas the advantage that hardly any exchanging operations are required.Moreover, the halogen lamp requires a light-adjusting filter, while theLED light source requires no light-adjusting filter. This is because,for example, in order to deal with differences in color in the base ofthe negative working film, it is only necessary to adjust the output ofeach of the LED light sources. Therefore, it is possible to simplify thestructure of the scanner device.

[0025] An optical fiber 13 for guiding light rays applied from therespective LED light sources 11 r, 11 g and 11 b is installed. Theoptical fiber 13 includes a red LED-use guide portion 13 r, a greenLED-use guid portion 13 g and a blue LED-use guid portion 13 b, andthese portions are joined into a joining portion 13 a, and outputted tothe photographic film F in a mixed color state. The light rays, appliedfrom the optical fiber 13, are allowed to pass through the photographicfilm F, and made incident on the CCD line sensor 2 through a converginglens 3. By transporting the photographic film F at a constant speed,image data corresponding to the frame images formed on the photographicfilm are successively acquired.

[0026] As shown in FIG. 2, the respective LED light sources 11 r, 11 gand 11 b are attached to LED substrates 10 r, 10 g and 10 b. Moreover,heaters 12 r, 12 g and 12 b are placed adjacent to (in parallel with)the line-shaped LED light sources 11 r, 11 g and 11 b. These heaters 12r, 12 g and 12 b are required so as to control the ambient temperatureat which the LED light-sources 11 r, 11 g and 11 b are placed to apredetermined range. As the ambient temperature changes, the LED lightsources 11 r, 11 g and 11 b also change in characteristics thereof, suchas light quantity and wavelength. Consequently, the quality of readimages deteriorates. Therefore, in the case when the LED light sources11 r, 11 g and 11 b are used as scanner-use light sources, it isnecessary to carry out temperature adjustments.

[0027] A control unit 4 (MPU) that controls the temperature-adjustingdevice is installed. The control unit 4 carries out controllingoperations on respective units in accordance with set programs.Light-quantity data, required for driving th LED light-source 11 r, 11 gand 11 b, are sent to a D/A conversion unit 7 from th control unit 4 sothat th respective LED light sources 11 r, 11 g and 11 b are driventhrough an LED driving circuit 6. The LED light sources 11 r, 11 g and11 b are driven and controlled by current-controlling operations.

[0028] Moreover, data, required for driving the heaters 12 r, 12 g and12 b, are sent to a D/A conversion unit 5 so that the respective heaters12 r, 12 g and 12 b are driven through a heater driving circuit 8. Therespective LED light sources 11 r, 11 g and 11 b and the respectiveheaters 12 r, 12 g and 12 b are installed on substrates 10 r, 10 g and10 b.

[0029] Furthermore, a cooling fan 20 for adjusting the ambienttemperature is installed. The ambient temperature is always monitored bya temperature sensor 9, and when the ambient temperature is out of apredetermined range, the cooling fan 20 is on/off controlled. Thecooling fan 20 is turned on (activated) by applying a predeterminedvoltage thereto. Voltage data are sent to a D/A conversion unit 21 fromthe control unit 4 so that the cooling fan 20 is driven and controlledbased upon a voltage applied thereto from a fan driving circuit 22. Asignal from the temperature sensor 9 for measuring the ambienttemperature is amplified in an amplifier 23. This signal is converted byan A/D conversion unit 24, and sent to the control unit 4. Based uponthese temperature data, the control unit 4 on/off controls the coolingfan 20.

[0030] <Temperature Adjustments>

[0031] The following description will discuss a specific methed foradjusting the temperature by the use of a temperature adjusting deviceas shown in FIG. 2. FIG. 3 shows a graph that explains the contents ofthe temperature adjustments, and the axis of abscissas indicates theelapsed time and the axis of ordinates indicates the ambient temperaturedetected by the temperature sensor 9. T_(D) represents a settemperature. T₃ represents a lower limit temperature of a permissiblerange. T₄ represents an upper limit temperature in the permissiblerange. Here, T₁ represents a temperature at which the cooling fan 20 isswitched off. T₂ represents a temperature at which the cooling fan 20 isswitched on.

[0032]FIG. 3(b) shows a graph that explains a conventional on/offcontrolling method. When the ambient temperature exceeds the upper-sideswitching temperature T₂, a voltage V is abruptly applied to allow thecooling fan 20 to start rotating abruptly. After the cooling fan 20 hasbeen driven, the ambient temperature is gradually lowered, and when theambient temperature goes lower than the lower-side switching temperatureT₁, the cooling fan 20 is switched off so that the applied voltagesuddenly drops from V to 0. Consequently, the operation of the coolingfan 20 is suddenly stopped. However, such abrupt on/off operations forthe applied voltage cause abrupt changes in noise, making the workersuncomfortable due to offensive noise to the ear. Moreover, when the LEDsare abruptly cooled, greater adverse effects due to changes in thecharacteristics are caused.

[0033] For this reason, controlling operations as shown in FIG. 3(c) arecarried out. In other words, when the ambient temperature exceeds T2,the applied voltage to the LED light sources 11 r, 11 g and 11 b isgradually increased. The time period is represented by Δt. The timeperiod is preferably set to 1 to 2 seconds. This is because the timeperiod of less than 1 second fails to eliminate offensive noise, whilethe time period exceeding 2 seconds causes degradation intemperature-controlling precision. Moreover, in the case when theambient temperature goes below T₁, the applied voltage is graduallylowered in the time period of Δt. Thus, the changes in noise aresmoothed so that offensive noise to the ear is eliminated. Moreover,since the LED light source is not cooled abruptly, it is possible toreduce changes in the characteristics of the LED.

[0034] <Time Chart>

[0035] Next, referring to FIG. 4, the following description will discussa time chart that is used when frame images in a photographic film areread by using the scanner 1. In FIG. 4, a photographic film is set inthe scanner 1 so that timing ti in which the film is transported isindicated. The completion of the transporting process is indicated byt₂. The LED light source is turned on at to prior to the start of thetransporting process of the photographic film, and is turned off at t₃after th c mpl ti n f th transporting procoss. Moreover, the heater isturned ff in synchronism with the turning-on of the LED light source(although not shown in FIG. 4, the on/off control of the heater has beenstarted upon carrying out a warming-up process of the photographicprocessing apparatus). The ambient temperature in which the LED is usedneeds to be always set in a predetermined range (T₃ to T₄). Thistemperature range is set to, for example, not less than 40° C. Thistemperature is slightly higher than the ambient temperature at which thescanner device is installed. Therefore, in order to maintain the ambienttemperature of the LED light source at a predetermined level, even whenthe scanning process of the photographic film is not carried out, theheater is maintained in the on-state during the corresponding time.Since, during the on-state of the LED light source, the LED itselfgenerates heat, it is not necessary to turn the heater on, and theheater is maintained in the off-state.

[0036] For the reason, as described above, the cooling fan 20 is alsocontrolled so as to be always operable. In other words, as shown in FIG.4, irrespective of the on/off operation of the heater, operationcontrols are carried out on the cooling fan. Thus, the ambienttemperature at which the LED light sources are placed is alwaysmaintained appropriately.

[0037] <Another Embodiment>

[0038] (1) The temperature adjusting device in accordance with thepresent invention is applicable not only to the cas in which an LEDlight source is used for a scanner device, but also to the cas in whichit is used for an exposing light source which exposes and prints animage onto a photosensitive material.

[0039] (2) The structure of a light path that directs light from the LEDlight source to a photographic film is not limited by the presentembodiment, and various modified embodiments may be proposed. Forexample, the light path structure may be formed by using not an opticalfiber, but a dichroic mirror and a prism.

[0040] (3) In the present embodiment, when the applied voltage isgradually raised or lowered, the voltage is linearly increased orreduced; however, the present invention is not intended to be limited bythis method. For example, the voltage may be increased or reduced in acurved manner. Moreover, the voltage may be increased or reduced bychanging the voltage step by step. The voltage may be changed in acombined manner between a straight line and a curved line. In short, thevoltage may be gradually changed within a range in which the functionsand effects of the present invention are properly exerted.

[0041] (4) The present embodiment has exemplified a case in which threeLEDs are used; however, in the case when a white-color LED is used, thestructure may include a single LED.

What is claimed is:
 1. A temperature adjusting device for an LED lightsource comprising: an LED light source; a temperature sensor fordetecting an ambient temperature of the LED light source; a cooling fanfor cooling the LED light source; a driving circuit for driving thecooling fan; and a control unit which on/off controls a voltage to beapplied to the cooling fan so as to set the ambient temperature within apredetermined range based upon results of detection by the temperaturesensor, characterized in that, upon on/off controlling the appliedvoltage, the control unit (4) is allowed to gradually raise/lower theapplied voltage.
 2. The temperature adjusting device for an LED lightsource according to claim 1, characterized in that the control unit (4)turns the applied voltage on when the ambient temperature exceeds anupper-side switching temperature (T2) that is set at a temperature lowerthan the upper limit of a temperature permissible range, and also turnsthe applied voltage off when the ambient temperature is lower than alower-side switching temperature (T1) that is set at a temperaturehigher than the lower limit of the temperature permissible range.
 3. Thtemperature adjusting device for an LED light source according to claim1, characterized in that the LED light source (11) is used for ascanner-use light source for reading frame images of a photographicfilm.
 4. The temperature adjusting device for an LED light sourceaccording to claim 3, further comprising: a line-shaped heater (12) thatis installed in the LED light source (11), and formed in a line shapealong the width direction of a photographic film (F) to be read so as tobe aligned adjacent to the LED light source (11) in the line direction,characterized in that the control unit (4) turns the heater (12) off insynchronism with the turning-on of the LED light source (11), and on/offcontrols the cooling fan (20) independent of the on/off operations ofthe heater (12).
 5. The temperature adjusting device for an LED lightsource according to claim 1, characterized in that the LED light source(11) is used for an exposure-use light source for exposing and printingan image onto a photosensitive material.
 6. The temperature adjustingdevice for an LED light source according to claim 1, characterized inthat the control unit (4) gradually increases/decreases the appliedvoltage linearly.
 7. The temperature adjusting device for an LED lightsource according to claim 1, characterized in that the control unit (4)gradually increases/decreases the applied voltage in a curved manner. 8.The temperature adjusting device for an LED light source according toclaim 1, characterized in that the time period in which the appliedvoltage is gradually increased/decreased is set to one to two seconds.9. The temperature adjusting device for an LED light source according toclaim 1, characterized by comprising: a red LED light source (11 r), agreen LED light source (11 g), a blue LED light source (11 b) thatconstitute a LED light source (11); a red LED guiding portion (13 r), agreen LED guiding portion (13 g) and a blue LED guiding portion (13 b)that guide light rays applied from the respective light sources (11 r,11 g, 11 b); and a joining portion (13 a) that allows the respectiveguiding portions to join to one another.
 10. The temperature adjustingdevice for an LED light source according to claim 1, characterized inthat the LED light source (11) is a white-color LED.